Human serum albumin (“HSA”) is used to stabilize botulinum toxin at high dilutions. This albumin is a human blood product-derived agent from pooled plasma collections. As the molecular weight of the material is low (69,000), filtration generally allows for excellent filtration sterilization, however, prions (non-nucleic acid dependent infectious agents) have become an increasing concern for both federal regulators and the general public. Most physicians and patients do not even know that there are human blood products within BOTOX™, the market leading botulinum toxin product. Prion dependent diseases include Creutzfeld-Jacob disease, Kuru, fatal familial insomnia, and Gertmann-Straussler-Scheinker disease. Although the incidences of these diseases are rare (one in 1,000,000), it has been estimated that one in 10,000 are infected with prions at the time of death. Prion diseases generally cause spongiforma encephalopathies of the brain with serious attendant neurologic symptoms prior to death. Humans are thought to acquire prions in two ways: (1) infection from medical procedures such as surgery, biologic agents, and tissue transplants, and (2) genetically. The impact that these observations have made is to try to limit human blood products in biologic agents.
Recently, recombinant albumin (RECOMBUMIN™) has become available via Delta Biotechnology LTD, (Nottingham, UK-Aventis-Behring LLC) via high yield yeast expression system, offering a synthetic alternative to human serum albumin and an important differential point. In clinical studies including 500 patients, there have been comparable immunity and allergic reactions to native HSA, although larger study figures may be available at this time.
HSA has been employed as a stabilizer in botulinum toxin since its introduction into clinical studies in 1981 (see Schantz E., Johnson E. Therapy with Botulinum Toxin, Mercel Dekker, New York, 1994). The purpose of the albumin protein in high concentration relative to the botulinum neurotoxin is to maintain structural and biologic integrity of the toxin during and after the dilution steps in manufacturing pharmaceutically acceptable doses. The albumin appears to bind (via non-covalent molecular interaction) with the neurotoxin, preventing adherence of toxin molecules to the glass containers and protecting the tertiary structures on the protein molecule from disruption when diluted in aqueous solution.
Botulinum toxin has been stabilized by a number of proteins, hence there are multiple opportunities to remove the human serum albumin from the formulation. Such proteins include, but are not limited to, animal based gelatins, ovalbumin, lysozyme, bovine and porcine albumins. HSA has been the preferred stabilizer primarily because of its low immungenicity. Anaphylastic or analphylactoid reaction, although possible, are low with use of human albumin compared to other protein stabilizers such as gelatins, which have reactivity rates as high as 0.5-1%. The reactivity rate of albumin has been estimated at less than 0.1%, although generalized urticaria syndrome has rarely been observed with human albumin, in a frequency similar to a common blood transfusion reaction. As gelatins have been associated with much higher local and generalized allergic reactions, these categories of proteins are not suitable excipients. Because of the need for repeated injections required to treat many clinical indications and uses, any stabilizing excipient in a botulinum toxin product must have a low immunoreactivity rate.
Infectious risks of HSA include hepatitis and other infectious agents, which have been eliminated for decades by pasteurization of pooled blood serum. As donor lots typically may come from as many as 50,000 individuals, rigorous standards of processing are necessary. As pasteurization does not eliminate prions, however such measures fo not eliminate the risk of transmission of prions by human blood products, such as HAS. Prion based disease transmission has been demonstrated by transfusing infected donor blood among animal species. In humans, possible transmission has been reported after corneal transplantation and other tissue transplantation procedures. It has been suggested that the disease can be genetically transmitted. The major public risks to prion-based diseases relate specifically to the inability to sterilize animal and human based products from the infectious agent. Conventional gas and heat sterilization have not been reliable, nor have filtration techniques such as those used to prepare botulinum toxin based pharmaceuticals.
Diseases identified to be caused by prions include Creutzfeld-Jacob disease, Kuru, fatal familial insomnia, and Gertmann-Straussler-Scheinker disease. Creutzfeld Jacob disease and its veterinary correlate (“mad cow disease”) is an encephalopathy which progressively impairs neurologic function causing seizures, dementia, somnolence, and death over a period of months to several years. Incubation periods may be as long as ten years so immediate analysis and elimination of sources of contamination may not be possible. Such a public health risk demands a strict approach to elimination of possible sources and opportunity for transmission. Recently, a blood donor to the albumin pool was reported retrospectively to have contracted Creutzfeld Jacob disease after having contributed to the albumin pool. Fortunately, no one appears to have contracted prion-based diseases to date from the use of human serum albumin within pharmaceuticals or when used as a plasma expander.
The incidence of prion based disease is rare (1:1,000,000) although it has been estimated that 1:10,000 autopsy analyzed human brains indicate infection at time of death. The pathology is described as a subacute spongiform change, which can be seen on microscopic examination of the neocortex. Even at a incidence of 1 per million, the chance that at least one blood donor contributing to the albumin pool over a twenty year period will be infected is high even with strict standards of screening. To date there are no validated tests to assess a blood donor for the syndrome. Many patients treated with botulinum based pharmaceuticals will need repeated injections over a twenty to thirty year period and so run a repeated risk of exposure.
In recent years, blood collecting centers have been mandated by regulatory agencies to screen for foreign travel exposure to areas where prion-related diseases have been reported, such as Great Britain, and such donors are excluded from the donor source for pharmaceutical grade albumin (see Reuters News Agency-1999 releases). Despite major worldwide effort to prevent international and intercontinental cross contamination, mad cow disease has recently been reported in Canada in May, 2003. The mode of transmission whether genetic or via contamination needs to be determined.
In recent years, there has been increasing consumption of botulinum toxin for cosmetic use as compared to its original medicinal indications, such as blepharospasm, spasmodic torticollis spasticity and other involuntary movement disorders. Because of the more casual use of this agent for cosmetic purposes, concerns arose over inadvertent exposure of large numbers of patients to human blood products via albumin. In past publications (Borodic GE Botulinum toxin issues and applications, Current Opinions in Otolaryngology, 1998 Dec. 5; 352(9143):1832), the disadvantages of human blood products within the vials of botulinum toxin were cited, especially relative to its use as a cosmetic agent. Physicians have not been routinely advising patients of the presence of human blood products although the major manufacturer of one form of botulinum toxin (BOTOX™) has listed the risk of possible prion contamination on its package insert.